7 – Add amp-video extension script not working

I am working on Drupal 7 amp theme and using validator tool https://validator.ampproject.org/

I am getting an issue while validating

“The tag ‘amp-video’ requires including the ‘amp-video’ extension JavaScript.”

amp-video code:

<amp-video class="embed-responsive-item" controls="controls" height="315" width="560" layout="responsive"><source src="https://democrm.indusnettechnologies.com/breathfree/sites/default/files/videos/AR_Asthma_connection.mp4" type="video/mp4"></amp-video>

I tried to add js extension script for amp-video but when I am checking view-source, I can’t find that particular line

<script async custom-element="amp-video" src="https://cdn.ampproject.org/v0/amp-video-0.1.js"></script>